Background: Early work on school readiness focused on academic skills. Recent research highlights the value of also including both children's social and behavioural competencies and family support. Aims: Reflecting this broader approach, this study aimed to develop a new and brief questionnaire for teachers: The Brief Early Skills and Support Index (BESSI). Sample: The main sample, recruited from the north-west of England, included 1,456 children (49% male), aged 2.5 to 5.5 years. A second sample consisting of 258 children (44% male) aged 3 to 5.5 years was recruited to assess the test-retest reliability of the BESSI across a 1-month interval. Methods: Following development and pilot work with early years teachers, a streamlined (30 items) version of the BESSI was sent to 98 teachers and nursery staff, who rated the children in their class. Results: The best-fitting model included four latent factors: Three child factors (Behavioural Adjustment, Language and Cognition, and Daily Living Skills) and one Family Support factor. The three child factors exhibited measurement invariance across gender. All four factors showed good internal consistency and test-retest reliability. Structural equation modelling showed that (1) boys had more problems than girls on all three child factors; (2) older children showed better Language and Cognition and Daily Living Skills than younger children; and (3) children eligible for free school meals (an index of financial hardship) had more problems on all four latent factors. Family Support latent scores predicted all three child latent factors and accounted for their correlation with financial hardship. Conclusions: The BESSI is a promising brief teacher-report screening tool that appears suitable for children aged 2.5 to 5.5 and provides a broader perspective upon school readiness than previous measures.